There have been known fuel cells in which the chemical energy obtained by reacting a hydrogen-containing fuel gas and an oxygen-containing oxidant gas with each other is transformed into electrical energy. In general, such fuel cells are formed by stacking a number of electricity generating cells in each of which the above-described chemical reaction is made to take place; each electricity generating cell has, for example, a structure in which a membrane electrode assembly is sandwiched by two sheets of separators.
Each of the plurality of the stacked electricity generating cells requires reaction gases (fuel gas and oxygen gas). Accordingly, in a fuel cell in which a plurality of electricity generating cells are stacked, gas flow paths for supplying reaction gases are formed, and the reaction gases are supplied to each electricity generating cell through the gas flow paths and the reaction gases are discharged from each electricity generating cell. In connection with this requirement, there have hitherto been proposed various techniques related to the stack structures of fuel cells which take into consideration the supply and discharge of the reaction gases.
For example, Patent Document 1 (Japanese Patent Laid-Open Publication No. 2003-338305) discloses a stack structure in which a dummy cell provided with an impurity removal function is disposed on one end of the stacking direction of a plurality of electricity generating cells. In this structure, the dummy cell functions as a filter to remove impurities from the reaction gases. In other words, the impurities contained in the reaction gases are removed by the dummy cell, and thereafter the reaction gases are supplied to the plurality of electricity generating cells. Consequently, the impurities (such as condensed water from humidified gas and metal ions from gas supply pipes) contained in the reaction gases are suppressed in flowing into the electricity generating cells, and the output power decrease is thereby suppressed.
Additionally, there is a possibility that the electricity generating cells are decreased in output power when the temperature is decreased, in association with generation of condensed water or the like. Accordingly, there has been proposed a technique related to a stack structure in which the temperature decrease of electricity generating cells is taken into consideration.
For example, Patent Document 2 (Japanese Patent Laid-Open Publication No. 2002-184449) discloses a technique to prevent the temperature decrease of the electricity generating cells by providing a terminal plate with an air chamber to function as a heat insulating layer; Patent Document 3 (Japanese Patent Laid-Open Publication No. 2005-19223) discloses a technique in which a dummy cell including a plurality of spaces is interposed between a terminal plate and an adjacent electricity generating cell and the dummy cell is used as a heat insulating layer; and Patent Document 4 (Japanese Patent Laid-Open Publication No. 2004-152502) discloses a technique in which an air layer to function as a heat insulating layer is formed between a terminal plate and an electricity generating cell.
As described above, there have hitherto been proposed various techniques related to functions such as a function to remove the impurities contained in the reaction gases and a function to prevent the temperature decrease of the electricity generating cells.